Electric machines, e.g., electric motors and generators, are used in a variety of industries to convert electrical energy to mechanical energy, and vice versa, for useful purposes. For example electric machines are used in the automotive, aviation, maritime, and other industries to operate aircrafts, helicopters, automobiles, boats, submarines, trains, and/or any other suitable vehicles.
To reduce fuel consumption and improve propulsive efficiency, it is generally desirable to use electric machines with large power densities, referred to herein as the electric machine's specific power or power-to-weight ratio. Electric machines having a high specific power may be smaller and more lightweight while generating equivalent or greater power than heavier electric machines.
Increasing the rotation speeds of electric machines is known to increase power-to-weight ratios. However, as the rotational speeds increase, the stresses on the various rotating components of the electric machine also increase. For example, certain electric machines use a disk retaining structure which allows for much higher tip speeds and power densities than conventional machines. However, as the rotor disk experiences large centrifugal forces during high speed operation, the rotor disk may creep or stretch slightly, which may affect the specific power of the electric machine.
More specifically, electric machines have an air gap between the rotor and the stator assemblies. The size of the air gap has an effect on the interaction of magnetic fields generated by the rotor assembly and the stator assembly, and thus on the performance and efficiency of the motor in general. During high speed operation, the rotor disk might stretch slightly, thus increasing the size of the airgap between a rotor and a stator, and affecting the specific power of the electric machine.
Accordingly, an electric machine with features for improving specific power and efficiency is desirable. More specifically, an electric machine with features for adjusting an air gap between a stator assembly and a rotor assembly to improve performance of the electric machine would be particularly beneficial.